1. Field of the Invention
The present invention relates to a piston pump having a feed mechanism.
2. Description of the Related Art
A brake fluid pressure controller for a vehicle is provided with an electronic control function such an electronic stability control function. A conventional piston pump used for the brake fluid pressure controller has itself a function for pressure-feeding a fluid to be drawn, into a pump chamber (e.g., JP Patent No. 3097726 B2 and JP Patent No. 3278982 B2, which correspond to U.S. Pat. No. 5,577,896).
In the piston pump, a circular groove portion is provided on an outer periphery surface of a piston, and a feed ring is attached to the circular groove portion so as to form a feed chamber between the feed ring and a housing. Furthermore, a valve portion is formed between the piston and the feed ring such that the feed ring abuts on or separates from the circular groove portion, thereby opening and closing an inlet passage of the feed chamber. When the piston is in a suction stroke, the valve portion is closed so as to pressure-feed the fluid in the feed chamber to a pump chamber.
In the piston pump described in JP Patent No. 3278982 B2, during a compression stroke of the piston, the fluid (liquid) having passed through the valve portion passes through a narrow clearance between the circular groove portion and feed ring and a passage inside the piston, and is drawn into the feed chamber. In contrast, in the piston pump described in JP Patent No. 3097726 B2, during a compression stroke of the piston, the fluid (liquid) having passed through the valve portion is drawn into the feed chamber through a slit passage that is provided on an end surface of the feed ring.
However, in the piston pump described in JP Patent No. 3278982 B2, a portion around the valve portion is throttled to have a smallest passage sectional area in a suction passage from a suction port to the feed chamber. When the temperature of the fluid such as a brake liquid (working oil) to be drawn into the pump chamber is low, the viscosity of the fluid becomes higher. In this case, the fluid feeding performance to the feed chamber through the smallest passage sectional area becomes deteriorated, and responding performance to a pressure increase is restricted.
In the piston pump described in JP Patent No. 3097726 B2, when the temperature of the fluid such as brake liquid (working oil) to be drawn into the pump chamber is low, the fluid feeding performance to the feed chamber through the slit passage on the end surface of the feed ring becomes deteriorated, and responding performance to a pressure increase is also restricted.